The present invention relates to an optical disk apparatus and a magnetic disk apparatus, and concerns especially an apparatus which retries reading when a read-out data error has occurred during reading operation, and relates, in particular, to a recording and reproducing apparatus which can recover from a read-out data error.
It is extremely important to read out the written data correctly for the information recording and reproducing apparatus, including the optical disk apparatus and magnetic disk apparatus. The major technological problem for the recording and reproducing apparatus is how to ensure the data reliability. To solve said problem, efforts have been made to improve the data reliability through the introduction of the error correction code (ECC). When the reliability of the optical disk apparatus is compared with that of the magnetic disk apparatus, read-out data errors of the optical disk apparatus occur more frequently that those of the magnetic disk apparatus. When read-out data errors have occurred, error recovery is carried out in order to avoid error recovery failure. The read retry operations are performed to implement said error recovery.
In the conventional read retry operation, the controller specifies the number of retries, and read operations are performed repeatedly when the read-out data errors have occurred. If error recovery still fails even after the read operation, the disk head position is deviated from the center of the track or the data strobe position is deviated from the normal position, then read operations are then repeated. To be concrete, said procedure is standardized for Enhanced Small Disk Interface (ESDI), which also serves as an interface.
The optical disk apparatus and magnetic disk apparatus are required to have higher and higher recording density every year, and severe requirements are imposed on reproduction of the readout data. That is, higher recording density requires reduced size and increased speed of signals read out from the recording medium, as well as reduced signal-to-noise ratio. To improve system performance, the disk apparatus tends to increase the number of revolutions of the recording medium in addition to the recording density. This has increased the speed of phase-synchronized clock pulses and writing clock pulses to identify the read-out data, and has reduced the read-out data reproduction margin.
In the optical disk apparatus, the data dropout is frequently caused by medium defects and dirt. Because of said data dropout, phase-synchronized clock pulses cannot be phase-synchronized with the read-out data, or phase-synchronized clock pulses deviate a lot from the specified frequency, making it difficult to identify the read-out data.
For the above reasons, read-out data errors occur frequently in the read operation, and the conventional technique has had a serious problem in that error recovery cannot be achieved.
An object of the present invention is to provide a recording and reproducing apparatus which has the function to recover from the read-out data error; said function has been absent in the conventional read retry operation.
The above object is accomplished according to the present invention by providing a recording and reproducing apparatus which comprises; (1) a drive circuit which provides driving so as to rotate a recording medium, (2) a recording circuit which records information on the recording medium rotated, (3) a reproducing circuit which reproduces the information from the recording medium rotated and which retries the reproduction of the information from an area in the recording medium where an error has occurred to the reproduced data in cases where such an error has occurred to the data reproduced in the process of reproducing information from the recording medium, and (4) a characteristic change circuit which changes a reproduction characteristic of the reproducing circuit, wherein the reproduction characteristic of the reproduction circuit is changed by the characteristic change circuit in cases where any error has occurred to the reproduced data in the process of reproducing information from the recording medium so that the reproduction circuit uses the changed reproduction characteristic to retry reproduction of information from the area in the recording medium where an error has occurred to the reproduced data.